The present invention is related generally to the field of microscopic examination of objects including specimen slides containing biological specimens. One important example of this is the identifying and counting of the different types of white blood cells found in a smear of whole blood as well as other evaluations which require microscopic optical analysis of the blood. Generally, in the past the task of finding, identifying and counting white blood cells along with the performance of tests such as evaluating red blood cell morphology, platelet sufficiency, and other commonly utilized studies has been a tedious and time consuming manual task. Recently, much effort has been expended in an attempt to automate one or more phases of the examination of blood smears. An automated, computerized scanning system that enables an operator to perform leukocyte differential counts, red blood cell morphology studies, platelet sufficiency estimates and other required evaluations is illustrated and described in the copending application of Adkisson, et al., Ser. No. 607,741 filed of even date and assigned to the same assignee as the present invention.
In providing a complete automated, computerized scanning system such as that described in the above-referenced co-pending application of Adkisson, et al., precise locations on the specimen slide as originally positioned on the slide carrier plate or tray may be stored for further reference. Thus, if a medical technician or other skilled operator desires to note a particular field of view for future inspection by a pathologist or other interested party, the precise x and y coordinate positions in the plane of the field of view along the perpendicular x and y axes may be noted for future reference. In accordance with that system, when desired, that precise x--y location may be recalled and utilized to actuate the microscope stage which, in turn, is driven thereto. If the object slide has been removed in the interim, however, it is necessary that the location of the object slide relative to the microscope stage location be precisely repeated upon subsequent replacement of the object slide on the slide tray such that the recalled field of view will correspond precisely to the same location on the slide itself. With the slide retaining means found in the prior art, the required precision, which may be within plus or minus 2.5 microns of the original position of the slide has not been possible.
The present invention, in particular, involves a system for precisely and positively positioning a microscope object slide in a repeatable manner relative to the movable stage of the microscope in an automated scanning microscope system.